Filter media having large interfiber pores and, thus, a high permeability typically contain sparsely packed relatively thick fibers. Such filter media require relatively low driving pressure to provide adequate filtration throughput rate and service life. However, highly permeable filter media, e.g., residential glass fiber HVAC filters, only provide a low filtration efficiency in that the large interfiber pore structures of the media do not have interstitial configurations that are suitable for entrapping fine contaminant particles. Consequently, coarse fiber, highly permeable, filter media have not been used in fine particle filtration applications.
In contrast, microfiber nonwoven webs, such as meltblown fiber webs, have been used as fine particle filter media. The densely packed fine fibers of these webs provide fine interfiber pore structures that are highly suitable for mechanically trapping or screening fine particles. However, the fine pore structure of meltblown fiber webs and other similar microfiber webs that have densely packed fine fibers results in a low permeability, creating a high pressure drop across the webs. Consequently, the low permeability of fine fiber filter media requires a high driving pressure to establish an adequate filtration throughput rate. Further, as contaminants accumulate on the surface of the filter media, the contaminants quickly clog the small interfiber pores and further reduce the permeability of the media, thereby even further increasing the pressure drop across the media and rapidly shortening the service life.
Additionally, microfiber web filter media do not tend to have a physical integrity that is sufficient enough to be self-supporting. Although the physical integrity of microfiber filter media can be improved by increasing the basis weight or thickness of the web, the increased basis weight or thickness exacerbates the pressure drop across the filter media. As such, microfiber web filter media are typically laminated to a supporting layer or fitted in a rigid frame. However, the conventional supporting layer or rigid frame does not typically contribute to the filtration process and only increases the production cost of the filter media.
There remains a need for integrated filter media that provide combinations of desirable filter properties, including high filtration efficiency and particle retention, high permeability, low pressure drop, high throughput rate and long service life.
In response to the discussed difficulties and problems encountered in the prior art, an integrated nonwoven laminate material suitable for use as a filter has been discovered. The integrated nonwoven laminate material includes a microfiber layer, a low loft multicomponent spunbond layer on one side of the microfiber layer, and a high loft multicomponent spunbond layer on the other side of the microfiber layer. The low loft multicomponent spunbond layer provides support and strength as well as filtration efficiency to the integrated nonwoven laminate material. Desirably, the low loft multicomponent spunbond layer has a basis weight of about 33-170 gsm, more desirably about 67-102 gsm. It is also desirable that the low loft multicomponent spunbond layer has a bulk density of at least 0.05 g/cm3, more desirably about 0.08 g/cm3 to about 0.14 g/cm3, still more desirably about 0.10 g/cm3 to about 0.13 g/cm3.
The high loft multicomponent spunbond layer acts as a prefiltration and dust entrapment layer as air enters the integrated nonwoven laminate material through the high loft multicomponent spunbond layer. The high loft multicomponent spunbond layer provides a structure for particulate accumulation, thus increasing the dust holding capacity and service life of the filter. As one example of a high loft material, crimped bicomponent spunbond fibers provide a higher loft relative to a low loft bicomponent spunbond layer. Desirably, the high loft multicomponent spunbond layer has a basis weight of about 33-170 gsm, more desirably about 67-102 gsm. It is also desirable that the high loft multicomponent spunbond layer has a bulk density less than 0.05 g/cm3, more desirably about 0.015 g/cm3 to about 0.035 g/cm3, still more desirably about 0.02 g/cm3 to about 0.03 g/cm3.
In accordance with one embodiment of this invention, the multicomponent spunbond fibers of the low loft multicomponent spunbond layer and the high loft multicomponent spunbond layer are bicomponent spunbond fibers having a lower melting point polymer component and a higher melting point polymer component desirably arranged in a side-by-side or sheath/core configuration. The high loft bicomponent spunbond layer may have lofted shaped fibers for enhanced dust holding capacity.
The microfiber layer contains relatively closely distributed microfibers. Desirably, the microfiber layer has a basis weight of about 10-34 gsm, more desirably about 13-21 gsm. It is also desirable that the microfiber layer has a bulk density of at least 0.05 g/cm3, more desirably about 0.08 g/cm3 to about 0.14 g/cm3, still more desirably about 0.10 g/cm3 to about 0.13 g/cm3. The microfiber layer may include a dual layer fiber web having a barrier layer and a bulky layer which results in a density gradient across the microfiber layer.
To produce an integrated nonwoven laminate material of this invention, the low loft multicomponent layer is formed, the microfiber layer is deposited onto the low loft multicomponent spunbond layer and the high loft multicomponent spunbond layer is deposited on the microfiber layer.
In accordance with one embodiment of this invention, the nonwoven laminate material having bicomponent spunbond fibers is then passed through a through-air bonding unit, wherein the nonwoven laminate material is heated to a temperature above the melting point of the lower melting point polymer component but below the melting point of the higher melting point polymer component, thereby causing the bicomponent fibers of adjacent layers to form interfiber bonds. As a result of the autogenous bonding of these bicomponent fibers, a single, cohesive integrated nonwoven laminate material is formed, which is suitable for use as a filter medium. In order to increase the attraction between particles being filtered and the filter fibers, any one or all of the layers of the integrated nonwoven laminate material may be electret treated (electretized), before or after the integrated nonwoven laminate material is formed. For example, the microfiber layer may be electret treated before it is deposited onto the low loft multicomponent spunbond layer.
With the foregoing in mind, it is a feature and advantage of the invention to provide an integrated nonwoven laminate material for filtration applications, which includes a microfiber layer disposed between a low loft multicomponent spunbond layer and a high loft multicomponent spunbond layer.
It is also a feature and advantage of the invention to provide a filter medium including the integrated nonwoven laminate material.